The present invention relates generally to semiconductor device processing and, more particularly, to a method for controlling linewidth in the manufacture of advanced lithography masks using electrochemistry.
Lithography is a well known technique for applying patterns to the surface of a workpiece, such as a circuit pattern to a semiconductor chip or wafer. This technique has the additional advantage of being able to faithfully reproduce small and intricate patterns. Traditional optical phololithography involves applying electromagnetic radiation to a mask having openings formed therein (i.e., a transmission mask) such that the light or radiation that passes through the openings is applied to a region on the surface of the workpiece that is coated with a radiation-sensitive substance (e.g., a photoresist). The other type of potential next generation lithography (NGL) mask is an extreme ultraviolet lithography (EUVL) mask. The EUVL mask works by reflecting and absorbing the incident radiation. For both types of masks, the mask pattern is reproduced on the surface of the workpiece by removing the exposed or unexposed photoresist. The capabilities of conventional lithographic techniques have been severely challenged by the need for circuitry of increasing density and higher resolution features. The demand for smaller feature sizes has driven the wavelength of radiation needed to produce the desired pattern to ever shorter wavelengths. Moreover, the International Technology Roadmap for Semiconductors (ITRS) projects (for both optical and next generation lithography (NGL) masks) a steady decrease in both the mean critical dimension (CD) and mean-to-target allowance on the mask. Currently on 90 nanometer (nm) masks, the CD mean-to-target is 7.2 nm for alternating masks and 9 nm for attenuating masks, while for the 45 nm node it decreases to 3.5 nm. Although write systems and etch technologies are expected to improve for the 45 nm node and beyond in order to make attaining this target more feasible, it is nonetheless a very difficult target to meet. Currently, feedforward and feedback control systems are being used in wafer processing to correct for CD variations. However, in mask production, mask quantities are much smaller and thus the feedback approach is not feasible. Typically, if a mask does not meet the CD mean-to-target, the mask is scrapped and a new mask is put into production. Not only is this expensive due to the cost of the raw materials and processing time, but turn around time is also significantly impacted.
As the technology nodes get smaller and smaller, these effects become even more important as the materials and processing costs become even higher and the degree of difficulty in manufacturing the masks increases dramatically. Accordingly, it would be desirable to be able to alleviate this problem by enabling the salvaging of the masks that would otherwise have been scrapped for linewidths that are larger than the mean-to-target.